This invention relates to Integrated Services Digital Networks (ISDN).
ISDN systems were developed to permit transfer of voice, data, and video information to each customer. The systems comprise three channels per customer designated the B1, B2, and D channels. The B1 and B2 channels each include 8 bits, while the D channel comprises 2 bits. A typical digital loop carrier transmission system, such as the Subscriber Loop Carrier (SLC.RTM.) system, generally transmits data within a remote terminal (RT) in a frame having 32 time slots of 16 bits each, with each time slot broken into 8 bits for voice/data and 8 bits for system information. A problem exists, therefore, in how to fit the 18 bits required in ISDN for each customer into the frame pattern of the standard carrier system. The usual approach now is to use three time slots for each customer with the B1, B2 and D channels, each occupying a different time slot. This solution, while generally workable, obviously wastes the true capacity of the system.
It has recently been suggested in telecommunications systems that the first time slot in each frame (time slot zero) be used to include bits from other time slots (see, e.g., U.S. Pat. No. 4,794,644 issued to Philip et al. and U.S. Pat. No. 4,873,682 issued to Irwin et al.).
It is, therefore, an object of the invention to utilize otherwise unused time slots, such as time slot zero, to create a data format which will tend to maximize the handling capacity of ISDN systems.